In the processing of ULSI etc., studies on pattern fabrication by radiation-induced graft copolymerization using radiation, such as X-ray, are in progress. This pattern fabrication typically comprises an exposure step of irradiating a predetermined region of a resist layer formed on a wafer through coating with radiation, a graft copolymerization step of introducing a monomer to graft-copolymerize the resist layer with the monomer, a development step of eveloping the resist layer to fabricate a predetermined resist pattern, and an etching step of etching the surface of the wafer by making use of the resist pattern as a mask. The feature of the above-described pattern fabrication resides in that the resist can sufficiently be exposed even when the exposure dosage to the resist is small, i.e., an enhancement in the sensitivity of the resist can substantially be attained. This feature enables the pattern fabrication process to be expedited, which makes it possible to attain high throughput.
Conventional pattern fabrication by radiation-induced graft copolymerization is described in, for example, Japanese Pat. Laid-Open No. 137671/ 1978 (corresponding to U.S. Pat. No. 4195108). In this literature, an example wherein poly(methyl methacrylate) (PMMA) is used as a resist is described. This resist is widely employed as a model resist in the field of lithography.
However, the above-described PMMA resist has a drawback that when the surface of the substrate is dry-etched by making use of the fabricated resist pattern as the mask, the mask per se is etched, i.e., the dry etching resistance is low. Therefore, an improvement in the dry etching resistance of the resist has been desired in order to put pattern fabrication by radiation-induced graft copolymerization to practical use.